94 



SECu 3. MEASUREMENT. 



right to left in the Figures. The parts of the escapement are : (1), a pallet C ; 

 (2), a lever D, having the same axis as C, and resting normally against a 

 fixed stop, from -which it can lift, but below which it cannot fall ; (it is in its 

 normal position in Figs. 1, 3, and 4) ; (3), an arm E, of which one end can 

 turn on a pin in D, and the other end, which is free, is lifted by the impulse 

 pins, and rests on them successively ; (it is resting on an impulse pin in 

 Fig. 1) ; (4), a first detent F, against which C sets when at the top of its 

 lift ; (C is thus set against F in Fig. 1) ; (5), a second detent G ; and (6), 

 set on a spring, a stop H, against which the scape wheel locks. 



The action of the escapement is as follows : Suppose (as represented in 

 Fig. 1) the scape wheel to be locked and that C has been lifted from its lowest 

 position through an angle a + ft to the top of its lift. . Suppose also that 

 the pendulum is moving to the right from the end of its swing g,t the left. 

 First, a slot or a pin in the pendulum rod (a pin is supposed here for sim- 

 plicity sake, and the path of the pin is shown by the dotted curve in each 

 Fig.) lifts G, idly, which falls back to its normal position, that of Fig. 1, 

 immediately the pin has passed ; then the rod itself, towards the end of its 

 swing to the right, impinges against a "beat" pin c in C, and, still rising, 

 carries C with it as far as it goes through a further angle 7. In rising 

 through 7, C takes up D with it, and the free end of E, which was resting 

 on the impulse pin by which it was lifted, is carried clear of that pin (now 

 see Fig. 2), and drops on to B 1 , th6 impulse pin next below, depressing F in 

 its drop, and afterwards holding F down (see E and F in same Fig.) . The 

 pendulum now returns, from right to left, and C with D falls back through 7, 

 D being arrested at the fixed stop ; the free end of its arm E still resting on 

 B 1 , and still holding F down.^The pendulum continuing its descent, C falls 



Fig. 1 The pallet against Fig. 2. At the end of the pendulum 



the first detent. swing to the right. 



